[mythtv-users] NFS and remote backend

Fedor Pikus fpikus at gmail.com
Sat Jan 12 01:37:40 UTC 2008

On Jan 11, 2008 5:20 PM, David Brodbeck <gull at gull.us> wrote:
> Just thought I'd add some notes on NFS tuning, since I had to do some
> recently.  I think the effects of some of the options on NFSv3 are
> widely misunderstood.
> On Jan 11, 2008, at 11:46 AM, Chris Pinkham wrote:
> > Share is async on the server.  It's for video only so I don't slow the
> > clients down by requiring sync when recording.
> Note that "async" greatly speeds up NFSv2, but with NFSv3 it just
> makes things riskier without much speed improvement.
> NFSv3 added data caching to the protocol.  An NFSv3 server in sync
> mode *won't* wait for the data to be written to disk during normal
> requests, but when the client issues an fsync() call or closes a file
> the server will wait until the data is written to disk before allowing
> the call to complete.  This is nearly as fast as async operation most
> of the time, and offers better data integrity.  Look at http://nfs.sourceforge.net/
>   and search for "safe asynchronous writes" for a good explanation.
> The client mount option to avoid in NFSv3, unless you really can't
> avoid it, is "noac".  That *really* slows down performance by
> disabling attribute caching.  If you can afford to have clients have
> slightly out-of-sync views of the filesystem you can lower overhead a
> bit by increasing actimeo.  For example "actimeo=3" will tell clients
> they can rely on cached data for up to 3 seconds.

Don't forget rsize and wsize: rsize=8192,wsize=8192.

Also noatime, which really should be the default for all filesystems :)
> Sorry to pontificate, but I just went through setting this up in a
> computer lab I maintain, about six months ago.  For a video share it
> doesn't really matter if you get a corrupted file when the server
> crashes, but when this happens to someone's home directory they get
> testy. ;)
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Fedor G Pikus (fpikus at gmail.com)

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